Some industrial processes call for the introduction of fluids into rotating tubes. In many such situations it is desirable, if not essential, that this be done without ambient matter becoming entrained with the fluid as it flows from a stationary conduit into the rotating tube.
For example, in constructing preforms from which optical fibers may be drawn, vapors of materials such as SiCl.sub.4, GeCl.sub.4, BCl.sub.3 and POCl.sub.3 are entrained in an oxidizing carrier gas such as oxygen. The vapor stream is then drawn through a stationary conduit and into a rotating glass preform tube. In order to inhibit the vapor stream from leaking to ambient atmosphere, and ambient air from entering and thereby contaminating the vapor stream, a rotary seal has been provided at the junction of the stationary and rotary tubes. This seal has been provided by locating an end portion of one of the tubes within an end portion of the other tube and positioning one or more resilient O-rings or washers between the two tubes. However, this arrangement has been less than satisfactory since at least one of the tubes is constantly rubbing against the resilient O-ring causing them to become heated and to wear out. Structural deterioration of the O-rings, of course, soon leads to leakage which is aggravated whenever, as here, there is a pressure differential between the fluid stream and ambient. Furthermore, in such highly controlled situations as optical fiber preform manufacture even a very slight leak can create severe problems. For example, a leak PPM to ambient surroundings can endanger personnel since the vapor stream is toxic. Such leakage also alters the rate of vapor stream flow into the preform which rate must be precisely controlled. Conversely, an ingress of ambient air will also alter the flow rate as well as contaminate the vapor stream with water vapor.
Thus, it is desirable to provide improved methods and apparatuses for supplying a rotating tube with fluid uncontaminated with ambient air such as is done in fabricating optical fiber preforms. It is this task to which the present invention is primarily directed.